Igniter and control means



Dec. 16, 1969 s. A. FLORIO ET AL 3,484,177

IGNITER AND CONTROL MEANS Filed NOV. 10, 1964 an /7 M 26% "I I E1 4:-- INVENTORS:

5AM A FL 0210,

Y M YLLIAM LEE/22mm. h 2/ nited States Patent 0 US. Cl. 431254 6 Claims ABSTRACT OF THE DISCLOSURE An electrical ignition system for a fluid burner having a solid state controlled conduction device which, when conducting, provides (1) a current path to energize a spark discharge device for ignition of the burner and (2) a current path to open a solenoid controlled, norma ly closed fuel line valve. An alternate current path provides sufficient current from the power source to hold the valve open. The system includes a flame sensing, temperature responsive resistance element which, when heated by the fuel flame, is effective to shut off the controlled conduction device, thereby Causing the spark discharge device to shut off. If the flame fails to activate the emperature responsive resistance within a predetermined time, a current responsive element is effective to open a normally closed switch to open the power circuit to shut off ignition and close the fuel line valve.

This invention relates to an ignition system for gas burning apparatuses and more specifically to an electrical ignition system using solid state components and which is adaptable for use in igniting the gas flame in gas dryers, oil furnaces, space heaters, and the like. The system of this invention includes not only an ignition means but also several safety devices which will prevent damage to the fluid burning apparatus due to malfunction of the electrical or gas components thereof.

An ignition system for gas-fired apparatuses such as clothes dryers or the like must be physically compact and insensitive to variations in humidity and temperature of the environment in which it is placed. Systems using solid state components have been found to be superior for these reasons and also because of the fact that such systems are subject to vibration and mechanical shock, particularly when used in a home clothes dryer installation. It is also important that any such ignition system include certain safety devices which will automatically shut off the flow of gas to the apparatus when the power supply temporarily fails and is resumed or when the flame, for one reason or another, is extinguished or fails to initially ignite.

Accordingly, it is an object of this invention to provide an electrical gas ignition system associated with a gas burning apparatus which is rugged, economical and dependable in operation.

It is another object of this invention to provide a gas ignition system for a gas-fired apparatus which includes automatic means for shutting off the gas flow to the apparatus if the power supply fails and for preventing subsequent gas flow upon the resumption of power until the ignition system is ready to re-ignite the gas.

It is another object of this invention to provide a gas ignition system for use with a gas burning apparatus which includes means for preventing the continual firing of the ignition apparatus if the gas fails to ignite after a predetermined interval.

It is a still further object of this invention to provide a gas ignition system for use with a gas burning apparatus which includes various means for shutting off the gas 3,484,177 Patented Dec. 16, 1969 ice flow to the apparatus upon the failure of certain components of the gas ignition system.

Other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, reference being made to the accompanying drawings in which:

FIGURE 1 is a schematic circuit diagram of a preferred embodiment of this invention showing only the electrical components thereof;

FIGURE 2 is a schematic circuit diagram of the second preferred embodiment of this invention with slight modifications in the ignition firing control circuit;

FIGURE 3 is a schematic circuit diagram of another preferred embodiment of this invention; and

FIGURE 4 is a schematic circuit diagram of yet another preferred embodiment of this invention.

It is to be understood that certain gas valves operated by solenoids schematically shown in these figures or other conventional fluid flow control devices are used with the ignition system of this invention which will be readily understood from the following description and need not be illustrated.

Referring to FIGURE 1, the control circuit is shown with line terminals 10 and 11 which are connected to a source of outside power, normally 117 volt AC housepower. It is to be understood that the gas igniter systems of this invention can be designed to operate on line voltage of different value but are illustrated herein as using 117 volt AC. A manually operated switch 12 in an upper line 13 1s provided for the operator to turn the system on and off and a normally closed switch 15, which is operated by a bi-metallic switch and its heater resistor 16 which will be described below, is also in the upper line 13 to stop the flow of current to solenoids 17 and 18 connected across lines 13 and 14. In certain installations, the manually operated switch 12 may be replaced by a thermostatically controlled switch, etc., if desirable.

Solenoids 17 and 18 control normally closed gas valves in the burner apparatus located in series in the gas supply line and which, when the solenoids 17 and 18 are not energized, are biased to a closed position to prevent the flow of gas. Solenoid 18, as shown, is connected directly across lines 13 and 14 and, when manual switch 12 is closed, will pull in to open its associated gas valve.

Solenoid 17 is connected across lines 13 and 14 through a resistor 19. Resistor 19 is selected such that its resistance is great enough to prevent sufflcient current flow through the solenoid 17 and resistor 19 to open its associated gas valve until another current path around resistor 19 is closed to increase the voltage across the solenoid.

The control circuit for the spark producing apparatus includes a silicon controlled rectifier (SCR) 20 having anode 21 and cathode 22 connected across lines 13 and 14 in series with the primary of a spark coil 23 and a capacitor 24.

A temperature variable resistor or thermistor 25 is connected in series with a resistor 26 across lines 13 and 14 and the control electrode or gate 27 of the SCR 20 is connected through the bimetallic switch heater resistor 16 to the junction between the thermistor 25 and resistor 26 as shown. The gate 27 of the SCR 20 is also connected to line 14 through an adjustable resistor or trimmer 28 and a solid state diode or rectifier 29 is connected between the anode 21 of the SCR 20 and the junction between solenoid 17 and resistor 19.

The thermistor 25, in the circuit shown in FIGURE 1, is a negative temperature coeflicient (NT C) type in which the resistance of the device decreases as its temperature increases. Such NTC thermistors are commercially available in a variety of resistance-temperature characteristics and'are compact,'economical and reliable. Thermistor 25 is physically located within the gas burning apparatus so that it is heated by the gas flame, schematically shown in FIGURE 1 at F.

The operation of the ignition control circuit of FIG- URE 1 is as follows: Manual closure of switch 12 puts full line voltage across solenoid 18 and pulls in the relay contacts associated therewith, opening its associated gas valve. As previously explained, solenoid 17 will not pull in at this time because resistor 19 limits the current through solenoid 17. The capacitor 24 charges and remains charged until the firing of the SCR 20. Firing of the SCR 20 is controlled by the voltage at its gate or control electrode 27 which is controlled by the voltage drop across the resistor 26 and the bi-metallic switch heater resistor 16 and the thermistor 25. These resistances are initially of such value that the voltage at the gate 27 will not permit the SCR 20 to fire until the charge on the capacitor 24 has reached an appreciable value and the voltage across the capacitor 24, primary of the spark coil 23 and the anode-cathode circuit of the SCR 20 is large enough so that, when the SCR 20 fires, a voltage in the secondary of the spark coil 23 will be induced to cause a spark across points S of a conventional igniter plug. In this manner, the intermittent firing of the SCR 20 produces sparks across the points S in the secondary of the spark coil 23 by periodically discharging the energy stored in capacitor 24 through the primary of the spark coil 23.

As previously stated, the resistor 19 is of a value large enough to prevent pull in of the solenoid 17 prior to the firing of SCR 20. As soon as SCR 20 assumes its conductive state a second low resistance current path is provided through the diode 29 and the anode-cathode circuit of the SCR 20. Resistor 19 is thus effectively shunted and the current flow through solenoid 17 is sufficient to pull in the solenoid and to open its associated gas valve 50 that gas now flows into the burners of the apparatus.

Upon ignition of the gas, a gas flame F heats the thermistor 25 and, as previously explained, reduces its resistance to decrease the voltage at the gate 27 of the SCR 20. Impressed voltage at the gate 27 of the SCR 20 is now of insuflicient magnitude so that the SCR 20 no longer fires and the ignition system stops for lack of current in the spark coil 23.

Solenoid 17 is selected so that the current through resistor 19 alone is suflicient to hold it in pulled-in position after the current path has once been established through the SCR 20, as previously explained, even though this current path opens when the SCR 20 ceases to conduct. In this state, the ignition circuit of this control system remains off and the flame continues to burn with solenoids 17 and 18 remaining pulled-in and their associated gas valves open.

Several important safety devices incorporated in the control circuit above described are as follows. First, as previously explained, solenoid 17 will not pull in to open its associated gas valve until the SCR 20 conducts to permit additional current through the solenoid 17. Thus, if there is a malfunction in the ignition system due to opening of the SCR 20, no gas will flow. Secondly, should a flame fail to be ignited for some reason, the thermistor 25 will not be heated and will remain at its normally high resistance value, causing current to flow through bi-metallic switch heater resistor 16 and the adjusting resistor 28. The bi-inetallic switch heater resistor 16 is and then resumes its normal value, the pull in of solenoid 17 and opening its associated gas valve will be delayed until the SCR 20 is again in condition to fire and produce an ignition spark. As previously explained, until the thermistor 25 has cooled to a point at which its resistance is large enough to trigger the SCR 20, the SCR 20 will not fire.

Several other fail-safe features of this system which provide for automatic gas shut off due to the failure of one of the components of the electrical system are as follows: 1) Opening resistor 26 or the circuit through the bi-metallic switch heater resistor 16 will prevent firing of the SCR due to the absence of a triggering voltage at the gate 27 and will therefore prevent pull in of solenoid 17 and opening of its associated gas valve, as previously explained. (2) Opening of the thermistor 25 will cause continued current flow through and subsequent heating of the bi-metallic switch heater resistor 16 which will open the normally closed switch 15 which in turn causes both solenoids 17 and 18 to drop out and shut otf the gas. (3) A short circuit between the gate 27 and the cathode 22 of the SCR 20 will prevent the SCR 20 from firing and thus the solenoid 17 would not open its associated gas valve, as explained, and continued current through the bi-metallic switch heater resistor 16 would open normally closed switch 15. (4) A short circuit in the diode 29 will establish a continuous discharge path for capacitor 24 and prevent sparking, and opening the circuit of the diode 29 will prevent pulling in of the solenoid 17 because the shunt path for resistor 19 will never be closed and, as previously explained, current flow through the solenoid 17 and the resistor 19 alone is insuflicient to pull in the solenoid 17.

Other safety features and advantages of this gas igniter circuit will be apparent to those skilled in the art and need not be further detailed.

FIGURE 2 illustrates a second preferred embodiment of the ignition system of this invention which is similar to that disclosed in FIGURE 1 and explained above except for the location and type of the thermistor element now designated 25a and the location of bi-metallic switch heater resistor 16. All other components of these control circuits are the same and have similar reference numbers. In this embodiment, a positive temperature coeflicient (PTC) thermistor 25a is connected in series with the bimetallic switch heater resistor 16 and the adjustable resistor 28 across lines 13 and 14. The gate 27 of the SCR 20 is connected between the PTC thermistor 25a and the adjustable resistor 28. In this embodiment, closing the manual switch 12 pulls in solenoid 18 to open its associated gas valve, and the voltage drop across bi-metallic switch heater resistor 16 and the PTC thermistor 25a is small enough such that the impressed voltage at the gate 27 causes the SCR 20 to fire in the manner previously described. When the PTC thermistor 25a is heated by the flame F, its resistance increases to a value to reduce the current flow through the bi-metallic switch heater resistor 16, thus preventing it from opening normally closed switch 15, and also causes the voltage at the gate 27 to be of a magnitude to stop further firing of the SCR 20. In other aspects, the operation and safety features of the control circuit of FIGURE 2 are identical to those previously described with reference to FIGURE 1.

FIGURE 3 shows another embodiment of the control system of this invention utilizing a SCR 20 and an NTC thermistor 25. In this embodiment, the winding for the solenoid of one of the gas valves consists of coils 17a and 17b connected as shown in FIGURE 3 and wound on the same core. In this arrangement, in which coil 17a is a helper winding for coil 17b, closure of manual switch 12 will pull in solenoid 18 to open its associated gas valve but the current flow through coil 17b, because of the presence of resistor 19 in series therewith, will not pull in its solenoid. The helper winding, or coil 17a, is connected across lines 13 and 14 in series with the bi metallic switch heater resistor 16 and the cathode-anode circuit of the SCR 20. As soon as the SCR 20 fires, current flow through the helper winding 17a, when combined with the force generated by coil 17b, will pull in the relay contacts and open its associated gas valve. In a manner similar to that described in the circuit shown in FIGURE 1, the SCR 20 and thus spark generated by the spark coil 23 will cease When the flame F has heated the NTC thermistor 25 so that its resistance drops and causes an impressed voltage at the gate 27 of the SCR 20 to prevent its firing. After the SCR 20 has ceased to fire, the current through coil 17b is sufficient to hold the solenoid in and its associated gas valve open. In this embodiment, the resistor 19 may be unnecessary as long as the ampere-turns in the winding 17b do not generate sufi'icient flux to pull in its relay without the help of helper winding 17a. As is the case with the previously described embodiments, failure of the flame to heat the NTC thermistor 25 and thus shut off the SCR 20 will cause current to heat the bi-metallic switch heater resistor 16 which opens switch and causes solenoids 17b and 18 to drop out their relay contacts, closing the gas valves. A set of normally open contacts 15a is closed by the switch 15 to shunt the spark coil 23 and prevent further ignition in the secondary.

A modified circuit similar to that shown in FIGURE 3 and capable of similar operation may include the same basic arrangement of components with the exception of the substitution of a PTC thermistor 25 connected be tween the lower terminal of the bi-metallic switch heater resistor 16 and the gate 27 of the SCR and an adjustable or trimming resistor 28 between the gate 27 of the SCR and line 14. Thus the positions of the thermistor and the adjustable resistor 28 are interchanged. This modified circuit, in which the thermistor 25 and adjustable or trimming resistor 28 are connected as shown in FIGURE 2, would operate in a similar manner as described therein.

In the embodiment shown in FIGURE 4, manual closure of the switch 12 will energize solenoid 18 and causes opening of its associated gas valve. Solenoid 17, however, will not pull in until the SCR 20 fires. When initially energized, the thermistor 25, which is an NTC type, has a high initial resistance such that the voltage on the control electrode or gate 27 will trigger the SCR 20 to a conduction condition. As previously described, conduction by the SCR 20 will create a spark in the secondary of the spark coil 23 which will ignite the gas. When the flame F heats the NTC thermistor 25 and reduces its resistance, it will shunt the adjustable resistor 28 to reduce the impressed voltage at the gate 27 of the SCR 20 to a value such as to terminate conduction of the SCR 20 and ignition by the spark coil 23. If the flame F fails to light, the continued flow of current through the SCR 20 to the bi-metallic switch heater resistor 16 will cause this element to open the normally closed switch 15 to shut off the gas at both valves and close normally open contacts 150 to by-pass the spark coil 23.

In each of the above-described ignition control system, a silicon controlled rectifier 20 has been used as the triggering component in the ignition system and is controlled by a thermistor 25 which senses the proper operation of the gas burning apparatus and functions to turn off the ignition system by affecting the gate or control electrode voltage of the SCR. It is to be understood that other components capable of these functions may be used in the above system and that the invention disclosed herein is not limited to use of these particular components. Any appropriate substitute for the thermistor, such as heat responsive bi-rnetallic switches, thermostatically actuated mercury switches, etc., may be used as the flame responsive element herein.

In addition to substitutions of the various components mentioned above, various modifications of the above described embodiments of the ignition system of this invention will be apparent to those skilled in the art and it is to be understood that such modification can be made without departing from the scope of the invention, if within the spirit and tenor of the accompanying claims.

What we claim is:

1. An ignition and control system in a fuel burning apparatus comprising, in combination,

(1) a power source of alternating current,

(2) a fuel burner with a fuel supply line connected thereto,

(3) a normally closed solenoid operated fuel valve in said fuel supply line with its winding connected to said power source through a current limiting resister,

(4) a fuel igniter,

(5) a controlled switching device having input, output, and control electrodes,

(6) a circuit connected across said power source and including (a) an energy storage device,

(b) the input and output electrodes of said controlled device, and

(c) said fuel igniter connected in series whereby periodic switching by said controlled switching device will energize said fuel igniter,

(7) means for increasing the current flow through said winding of said solenoid when said controlled device is conducting whereby said increased current will cause said fuel valve to open,

(8) means responsive to the ignition of said fuel and operably connected to said control electrode of said controlled device and eifective to render said device non-conductive subsequent to the ignition of said fuel, and

(9) current responsive means operatively connected to said control electrode of said controlled device effective to open the power circuit to said controlled device and to the winding of said solenoid after a predetermined duration of the periodic switching by said controlled device.

2. The ignition and control system of claim 1 wherein said means responsive to the ignition of said fuel elfective to render said controlled device non-conductive comprises a flame-sensitive, variable resistor which, when exposed to the flame from ignited fuel, causes a voltage variation at the control electrode of said controlled device effective to render said controlled device non-conductive.

3. The ignition and control device of claim 2 wherein said flame-sensitive, variable resistor has a negative temperature coefiicient.

4. The ignition and control system of claim 1 wherein said current-responsive means effective to open the power circuit to said controlled device and said solenoid winding includes an electrically-heated, bimetallic elernent effective to open a normally closed safety switch after a predetermined duration of periodic switching by said controlled device.

5. An electrically-operated burner system comprising a burner, a fuel line connected thereto, an electricallyoperated means for controlling flow of fuel to said burner, a spark igniter associated with said burner, a transformer having a primary and a secondary winding with said secondary winding connected to said spark igniter, an electrical power supply, a variable conduction device having input and output main terminals as part of a single main conduction path and a control terminal, an energy storage device, a circuit connecting said energy storage device, said transformer primary and said input and output terminals in series across said power supply whereby conduction by said variable conduction device will energize said spark igniter, means for activating said fuel control means when said variable conduction device is conducting to supply fuel to said burner, and circuit means connected to said control terminal of said variable conduction device including a flame-sensing device located to monitor flame from said burner and elfective to prevent conduction by said variable conduction device after ignition of fuel at said burner.

6. An ignition and control system in a fluid-burning apparatus comprising, in combination, a power source, an electrically-operated means to control the flow of fluid to said apparatus and connected to said power source, means to control the flow of energizing current to said electrically-operated means including a siliconcontrolled rectifier in the presence of a flame, and a norcapacitor connected in series across said power source with said controlled rectifier whereby conduction by said controlled rectifier causes a discharge of energy into said spark coil from said capacitor, a flame-responsive variable resistance and a current-responsive element operably connected to the control electrode of said silicon-controlled rectifier acting to prevent conduction by said siliconcontrolled rectifier in the presence of a flame, and a normally closed safety switch actuated by said current-responsive element to Open the circuit to said electricallyoperated means upon failure of said flame-responsive variable resistance to perform its control function.

References Cited UNITED STATES PATENTS 1,858,265 5/1932 Dahlstrom 15828 2,171,955 9/1939 Sullivan 15828 3,007,080 10/1961 Benson 315240 X 3,136,877 6/1964 Heller 219499 3,204,685 9/1965 Patrick 158125 3,215,818 11/1965 Deaton 219499 3,238,992 3/1966 Forbes 158128 X 3,251,351 5/1966 Bowers 123i48 EDWARD G, FAVORS, Primary Examiner 333 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatenrNo. '5 48L 177 Dated December 19, 1969 In n fl Sam 9, 31 1 ggd William J. Roberts It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 9 delete "1n the presence of a flame, and

a nor-' and insert a spark coil and an energy storage SIGNED RND SEALED MAY 5 .1970

' WILLIAM E "m an. Edward m 1 Commissioner of Patents Attesting Offiw 

